Reducing the diameter of the terminal-side end area of the glow tube of a glow plug by rotary swaging is known, in which a central, solid and sealing connection of the end of the glow tube to the projecting inner pole of the glow plug will be achieved without damage of the gasket which is located in this area.
To do this, rotary swaging machines which are also called hammering or reducing machines are used which reduce the outside diameter in an advance process by forming under compressive a conditions with a relatively high speed working pulse sequence and thus close the glow tube filled with the inner pole and insulator via the gasket.
Rotary swaging machines use tools which radially oscillate via rams with high working frequency form the workpiece located in the center of the tools accordingly. In doing so then a high-speed, brief forming stroke of the tool is transmitted to the workpiece located in the center when a ram pair passes under the roller pair. Between the strokes the rams and tools are opened by centrifugal force and the workpiece continues to be inserted axially. The tolerances which can be achieved in rotary swaging in a cold working process are +/-0.01 mm.
The original outside diameter of the glow tube is reduced in a certain length to a certain amount which is conventionally not yet the final amount, and thus sits stationary on the inner pole, sealing element and insulating material. The connection which has been produced hereby must be of a bulk nature for the next working process which relates to reduction of the heating rod to its final size.
The high noise evolution which necessitates the noise control booths is disadvantageous in the rotary swaging process and rotary swaging devices known from the prior art. The noise evolution is caused by the necessary high ram frequency which is caused by the low forming per stroke of the rotary swaging machine. The friction portion of the workpieces in the tools must be great to prevent the workpiece from being expelled from the tools opposite the feed direction. The noise arises especially at the locations at which the rams hit the rollers, tools hit the workpiece, and in idle, the tool halves of the rotary swaging devices hit one another.
In addition, due to the large radial and axial loading of the end area to be machined in the glow tube there is the danger of damage of the sealing elements located in it, for example by overstretching.